1. Field of the Invention
The present invention relates to a semiconductor memory device, and more particularly to a semiconductor memory device that operates using, for example, initialization data.
2. Description of the Related Art
Semiconductor memory devices for use in mobile apparatuses, such as cell-phones, employ a technique for reducing the consumption of power during a standby state by cutting the current paths of peripheral circuits connected to a memory cell array and memory bank that are not accessed. In these semiconductor memory devices, the peripheral circuits that are not accessed are set in a low power-consumption state called a sleep mode. To realize the sleep mode, a switching element (e.g., a transistor) is provided across each current path, and is turned on or off to close or open each current path.
A redundancy function for rescuing a defective cell in a memory cell array using a redundancy-circuit is well known. Redundancy data used for the redundancy function is, for example, transferred, upon turn-on of the power supply, from a nonvolatile element provided outside a semiconductor memory device.
When the sleep mode is employed for a semiconductor memory device having such the redundancy function, the consumption of power can be reduced by interrupting the supply of current to peripheral circuits (such as a sense amplifier circuit, DQ buffer, column redundancy circuit, IO buffer and row decoder). However, if the current path of a circuit that latches row redundancy data is cut, the row redundancy data is lost. In this case, initialization processing must again be performed, therefore a considerable time is required to recover the device. Further, initialization processing itself inevitably interferes with access to a memory cell array or other macros that are not in the sleep mode.
Latch circuits that must retain data in the sleep mode include, as well as that for redundancy data, a latch circuit for, for example, data used to control operation timing or an operation voltage. In particular, in the case of dynamic random access memories (DRAMs), a large number of data items must be retained in the sleep mode. Therefore, unless the supply of current to the circuits that retain the data items is interrupted, reduction of power consumption in the sleep mode cannot be realized.
A semiconductor integrated circuit having a data retaining function for reducing the consumption of current is disclosed as a technique relevant to the above (see Jpn. Pat. Appln. KOKAI Publication No. 2002-56671).